PAST AND PRESENT

Apr 1, 2000 12:00 PM, Wolfgang Ahnert, Jim Brown and Helmut R. Grothe

Integrating a high-quality, expandable digital audio system at the Deutsche Oper Berlin.

In its original form, the Deutsche Oper was inaugurated in November 1912 in the historic Charlottenburg section as Deutsches Opernhaus (German Opera House). The facility was rebuilt after World War II, and the main performance space reopened on September 24, 1961. The new building was designed by the architect Professor Fritz Bornemann in the style of the late 1950s, and it included parts of the original structure that had survived the war.

The main performance space seats 1,885 spectators with balconies and side boxes at two levels. The reverberation time of about 1.5 seconds was optimized by Professor Cremer in 1961 for operatic performance and was achieved without the use of electronic enhancement simply because it was not available at the time.

Work on installation of new systems began in 1989 and is still currently underway. One of the greatest challenges has been the sheer size of the facility and its performance spaces; Deutsche Oper Berlin occupies approximately 172,000 ft superscript 2 (16,000 m superscript 2) and has a building volume of more than 10,600,000 ft superscript 3 (300,000 m superscript 3), including the main audience chamber, stage house, rehearsal stages, orchestra room, workshops, storage and administration.

Sound reinforcement solutions

The first part of the new sound system was installed in 1989. In the lateral portals (the cheek walls flanking the forestage) a 4 2 array of high-performance compact loudspeaker systems (d&b Audio F1220) was installed, appropriately inclined and swiveled one on top of the other to provide the required coverage (Main Group 2 in Figure 1). Over the proscenium, an additional 2 2 array of the same loudspeaker systems was arranged side by side (Main Group 1 in Figure 4). The job was not to radiate much sound to the side walls but to supply a full sound to the audience. The d&b Audio F1220 is a two-way system that is well regarded in Germany in theatre applications, and it works quite well at Deutsche Oper Berlin. To help supply a stereo image, the existing finish covering the side walls of the forestage has been replaced by a new, acoustically transparent net grid composed of thick wire spaced by about 1 inch (25.4 mm). Behind this visually opaque grid can be hidden some sound reflectors to supply short time reflections back to the musicians within the orchestra pit. Figure 2 shows the direct sound level mapped over the audience areas. Although the calculation includes interference and shadowing, it shows a good and smooth direct sound coverage. Because listeners in areas A14 and A15 are sitting in separate boxes that are partially shadowed from the proscenium clusters, these boxes must be covered with separate small ceiling loudspeakers.

One compromise made during this initial upgrade was to allow direct sound levels in the upper balcony (audience areas A13 and A13*) to fall off a bit due to the inverse square law. During the next stage of work, additional loudspeakers (Main Group 3) will be installed to provide a bit more direct sound to this area, thereby supplementing the inverse square loss of the proscenium loudspeakers. It will not be necessary to re-aim some of the existing loudspeakers when the new loudspeakers are installed.

To cover the first rows of the audience, connection sockets for additional loudspeakers were installed in the vertical face of the stage. These may also be used for connecting portable loudspeaker systems, such as foldback (stage monitor), a speaker's desk and precedence loudspeakers built into a podium.

The main reinforcement system can provide 10 W to 15 W, which corresponds to a maximum SPL of 105 to 107 dB in the diffuse field of the auditorium (with L subscript r = L subscript W - 10 log V/ft superscript 3 dB + 10log RT/s + 29.35 dB). A key design criteria was good intelligibility for speech and good clarity for music. Figure 3 shows the expected values for AL subscript cons that have been confirmed by measurements of the installed system at key locations.

In 1991 new systems for performer foldback (stage monitoring) and sound effects precedence were installed in the stage area (Main Groups 4, 6 and 8). Main Groups 5 and 7 are to be installed during the next development phase. The d&b model F1220 will be used for Groups 6 and 8, d&b model B1 (sub-woofer, 32 Hz to110 Hz) and d&b model F2 (137 dB maximum level, 60 40, 2 inch horn and 20 12 0 or 51 mm 305 mm cone loudspeaker) for Main Group 4.

Signal distribution, routing and mixing

Next in the order of priorities was an extensive system for routing and distribution of mic and line level audio signals around the performance and rehearsal spaces. From the beginning, it was decided that a fully digital system would provide the greatest flexibility and highest level of performance.

The design team at Acoustic Design Ahnert (ADA), consultants for the project, decided to try to integrate the mixing system with the signal distribution system. They used a mixing console that could operate fully in the digital domain, take its inputs as digital signals from the routing system, perform all signal processing in the digital domain and return its outputs to the routing system still in the digital domain. The systems chosen for the project were the Nexus routing and distribution system and Cantus mix consoles, both products of the German manufacturer, Stage Tec. The mixing consoles contain no analog or digital audio electronics; they are control surfaces for the centrally located DSP and routing electronics. Two mix consoles were designed into the system. One usually resides in the control room for the main performance space where it is primarily used to mix for sound reinforcement, surround sound, the hearing-impaired system, and performer foldback (stage monitors). The other resides in the rehearsal hall's control room and is used to record rehearsals and performances in both spaces and to play back music and effects for rehearsals. The two consoles are identical and interchangeable via the routing system, and are thus able to act as spares for each other.

The physical configuration of the routing system is built around what Stage Tec calls a "Base Device," a 3 RU, 19 inch (483 mm) frame that contains 20 free slots to house the different input and output boards at each location. Available formats are analog in (mic and line), analog out, AES, SPDIF, SDIF-2, Y2, MADI, ADAT, TDIF and digital mic (AES with phantom power). Furthermore, a signal processor board and different transmission boards for data and GPI/GPO are available. All these different formats are converted into a common format that is similar to the AES format but contains some information to synchronize the system and to carry remote control data. These signals are routed throughout the entire network. So the complete system is always synchronous and requires no additional format converters to work with the different signals that may occur in the facility.

The Cantus consoles are essentially control surfaces that allow users to manipulate mixing and signal processing functions that are implemented in DSP. They combine the best of both worlds, using displays, indicators, switches, and controls that are all assignable to nearly any imaginable function, depending on the needs of any given production. Virtually every element of the console is freely assignable - the audio channels as well as the user surface. All knobs work in combination with displays that show the selected parameter and its value in analog and digital form.

The audio signal processing of the mixing consoles (for input channels, groups, sums and AUX sums) is designed for 90 audio channels plus monitoring. Every input and output of the entire Nexus network can be connected to both of the consoles. Thus, the operator can mix any combination of mics and line level or digital sources to any combination of output busses and then assign those busses to any channel of the sound reinforcement, effects playback and stage monitor systems.

The console has its own fiber optic connection to the central processing unit, but for the most part, this connection carries only control signals. The only audio signals at the desk are those used to drive headphones and control-room monitor loudspeakers, which sit atop the overbridge.

Overall configuration of the routing and distribution system is a networked function, and it can be achieved from any of the control locations. At each of the base devices (I/O racks), a control PC can be connected via serial interface (RS-232 and RS-422). A special protocol is used. Basic adjustment and configuration at the consoles are done via an integrated graphics tablet or keyboard and graphically shown on the TFT monitor installed in the meter bridge plane. All audio settings have to be effected through the controllers and switches of the operating channels faders by means of the keyboard.

Stage management and utility systems

To facilitate operation of these systems, it was decided to integrate the user interface for all of them (intercom, call lights, voice paging, program monitoring and video) into principal user stations at selected locations. Primary control locations chosen were downstage right, downstage left, the control rooms, the in-house mix location, and the central equipment rack (in the basement). The greatest operational control would be required at the two stage management positions, downstage left and right. At other primary locations, multi-key, table-mounted master stations would be required. The remaining locations would need simpler portable stations, such as a belt pack or compact loudspeaker station. All stations required a built-in mic, loudspeaker, a headset jack and two-color light-signaling devices. The great number of rooms to be covered by these systems and the complexity of the control functions required for each dictated the use of a computer-based control system for the combined systems.

Intercom stations (18 permanent and more portable ones) would be needed throughout the performance spaces and in work areas, and nearly 400 loudspeakers would be required throughout the building. All central electronics for the system would be housed in the main equipment room in the basement. The intercom system should provide configurations for more than 20 simultaneous party-line conversations with any user station assignable to any group. The stage manager and the director also needed a wireless user station so that he could act from different places on stage, for commands to groups or rooms that are routed first on the stage manager console and to listen to his intercom-circuit.

Salzbrenner, Hallstadt, Germany, was chosen as the contractor for the stage management system. Hardware for the intercom system was designed and manufactured by Salzbrenner and StageTec. The stage manager consoles, all intercom stations, and light signaling components are custom products by Salzbrenner. Audio routing uses a StageTec Nexus frame with A/D and D/A converters. The video routing system uses four units of the Ernitec System 1000M.

The intercom signal is transmitted digitally over standard four-pair CAT5 UTP cable to each user station. The cable also carries DC power for all but the largest user stations. Each user station (master station, loudspeaker station, beltpack or portable signal light) is addressable. The four-pair buss cabling (CAT5 UTP type), wired party-line style (circulating to all stations as opposed to a dedicated home run to each station) carries the control signals, monitoring of the 100 V distributed paging system and paging access to the 100 V distributed for stage manager call (for example, back of house paging).

An all-call voice-paging system provides for the transmission of preprogrammed announcements from the intercom system's digital speech memory and live announcements from any of the primary intercom stations. In case of emergency or evacuation, it is possible to activate the paging system with overriding priority. Via the independent power supply of the central unit, the system also remains operable in case of main power failure for emergency announcements for the required period of 30 minutes. There is no backup power for the reinforcement system.

Voice paging and performance sound from the auditorium and the stage is transmitted to various rooms throughout the building on a multizone 100 V distributed system. Most rooms have performance sound with voice paging override, but some areas (floors and open areas) have paging only. Performance sound can be individually controlled in each room, but paging cannot.

To provide program sound, a total of 11 mics are installed at various locations around the stage and audience chamber. Because the stage is so large, more than one stereo pair is often used; the sound operator builds the required mix of these mics for any given production. A mono sum is used to feed the distributed 100 V system, the hearing-impaired system, and the stage management (intercom) systems.

At locations where more critical listening is required, the room monitor mics are fed as a +6 dBu line level signal (the nominal level of European broadcasters) and reproduced on active monitor loudspeakers. In addition to the control rooms, the line level signal is used at director positions, and can be sent elsewhere as needed by the audio router.

The new video system includes all new wiring and routing infrastructure, and remotely controlled cameras have been installed in the auditorium and stage areas. Three closed-circuit channel modulators can be dedicated to distribution of these cameras, allowing up to three different cameras (or any other video program) to be viewed simultaenously via the in-house broadcast cable system. Images can also be routed to networked PCs via the house's Ethernet connection. The video transmission system includes a character generator, which is used to display a programmed sequence of numbers to indicate the progress of the production (called "integrated act indication"). The stage manager can select any number (an act or scene number, for example), which is then inserted into the desired video feeds.

A total of six cameras are currently in use and can be switched to feed any of the three RF video modulators.

In addition to the RF distribution system, certain users (technical director, stage managers, sound operators, light controllers or directors) can view any of the video sources via their own dedicated baseband composite video feeds directly from the video crosspoint switcher. The system is capable of handling RGB, RGBHV and digital video, but with the exception of feeds to the computer network, only composite video is currently supported at input and output locations. The routing electronics for this system are installed in the basement rack room.

In the wings downstage right and left, there are two identical stage manager consoles. The consoles may be used individually, in combination or in a redundant mode for coordinating the performance flow. From each, the stage manager can view and control any of six (one is in standby) video cameras, listen and talk to all configured matrix points, control more than 40 light signs, control the back of house paging system, and make announcements to both front of house and back of house areas.

This new computer network enables a universal exchange of sound programs within the opera house, which it is hoped will be expanded to include other houses of the city of Berlin.